Mysql查詢與條件的另一列

Question

這是我的第一個問題，所以我希望我不要搞砸了。

這裏有一個SQL小提琴我提出幫我解釋一下：http://sqlfiddle.com/#!9/7f2b5c/7

我們有問題，答案question_types和answer_types。

我想知道每個問題，有多少人已經回答了每個answer_type以及有多少人回答了這個問題，但是我無法獲得總數。

這就是我得到：

id | fk_question_type | description   | num | value  | total 
1 | 1    | How was the breakfast? | 0 | Bad  | 0 
1 | 1    | How was the breakfast? | 1 | Good  | 1 
1 | 1    | How was the breakfast? | 0 | Indifferent| 0 
1 | 1    | How was the breakfast? | 2 | Very good | 2 
2 | 1    | How was the lunch?  | 0 | Bad  | 0 
2 | 1    | How was the lunch?  | 1 | Good  | 1 
2 | 1    | How was the lunch?  | 0 | Indifferent| 1 
2 | 1    | How was the lunch?  | 1 | Very good | 1 

這是我想什麼：

id | fk_question_type | description   | num | value  | total 
1 | 1    | How was the breakfast? | 0 | Bad  | 3 
1 | 1    | How was the breakfast? | 1 | Good  | 3 
1 | 1    | How was the breakfast? | 0 | Indifferent| 3 
1 | 1    | How was the breakfast? | 2 | Very good | 3 
2 | 1    | How was the lunch?  | 0 | Bad  | 2 
2 | 1    | How was the lunch?  | 1 | Good  | 2 
2 | 1    | How was the lunch?  | 0 | Indifferent| 2 
2 | 1    | How was the lunch?  | 1 | Very good | 2 

查詢我想現在：

SELECT id, fk_question_type, description, num, value, SUM(num) AS totalAnswers 
FROM (
    (SELECT q.id, q.fk_question_type, q.description, COUNT(a.id) AS num, at.value 
    FROM answer a 
    LEFT JOIN question q ON a.`fk_question`=q.`id` 
    LEFT JOIN answer_type at ON at.id = a.`fk_answer_type` 
    GROUP BY q.id, at.id ORDER BY q.id, at.id) 
    UNION ALL 
    (SELECT q.id, q.fk_question_type, q.description, 0 AS num, at.value 
    FROM answer a 
    LEFT JOIN question q ON a.`fk_question`=q.`id` 
    LEFT JOIN answer_type at ON at.fk_question_type=q.fk_question_type 
    GROUP BY q.id, at.id ORDER BY q.id, at.id) 
) AS T 
WHERE fk_question_type = 1 
GROUP BY id, value ORDER BY id 

如何在保留其他列的同時彙總具有相同ID的行的數量？

Answer 1

使用子查詢獲取每個id的總和，並將其與通過獲取每個值行的查詢進行連接。

而且在外部查詢，你應該使用SUM(num)或MAX(num)到num值從UNION合併這兩個查詢。

SELECT T.id, fk_question_type, description, SUM(num) AS num, value, T2.totalAnswers 
FROM (
    (SELECT q.id, q.fk_question_type, q.description, COUNT(a.id) AS num, at.value 
    FROM answer a 
    LEFT JOIN question q ON a.`fk_question`=q.`id` 
    LEFT JOIN answer_type at ON at.id = a.`fk_answer_type` 
    GROUP BY q.id, at.id ORDER BY q.id, at.id) 
    UNION ALL 
    (SELECT q.id, q.fk_question_type, q.description, 0 AS num, at.value 
    FROM answer a 
    LEFT JOIN question q ON a.`fk_question`=q.`id` 
    LEFT JOIN answer_type at ON at.fk_question_type=q.fk_question_type 
    GROUP BY q.id, at.id ORDER BY q.id, at.id) 
) AS T 
JOIN (SELECT q.id, COUNT(*) AS totalAnswers 
     FROM answer a 
     LEFT JOIN question q ON a.`fk_question`=q.`id` 
     LEFT JOIN answer_type at ON at.id = a.`fk_answer_type` 
     GROUP BY q.id) AS t2 ON T.id = T2.id 
WHERE fk_question_type = 1 
GROUP BY T.id, value 

DEMO